UISegmentControl分段控制器是UIKit框架提供的一组按钮栏，提供多个可选的按钮，只能激活其中的一个，响应事件。主要用来在同一层次重要性下不同的信息展示或者不同的界面展示之间切换。例如手机QQ的主界面的消息和电话两个选项卡。
我们看一下UISegmentedControl的继承结构：
UISegmentedControl-->UIControl-->UIView-->UIResponder-->NSObject
在iOS事件相关类中我们知道UIControl将触摸事件转换成了带接收方的控件事件，它本身是个抽象类，只能实例化它的子类来处理控件事件。UISegmentedControl继承自UIControl,它具有所有UIControl的属性和方法。
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属性
@property(nonatomic) UISegmentedControlStyle segmentedControlStyle NS_DEPRECATED_IOS(2_0, 7_0, "The segmentedControlStyle property no longer has any effect") __TVOS_PROHIBITED;
@property(nonatomic,getter=isMomentary) BOOL momentary; // if set, then we don't keep showing selected state after tracking ends. default is NO
@property(nonatomic,readonly) NSUInteger numberOfSegments;
@property(nonatomic) BOOL apportionsSegmentWidthsByContent NS_AVAILABLE_IOS(5_0);
@property(nonatomic) NSInteger selectedSegmentIndex;
@property(null_resettable,nonatomic,strong) UIColor *tintColor;
iOS7之后采用扁平化设计风格，segmentedControlStyle被废弃，设置了也没有效果。momentary设置点击之后是否恢复原样，默认是NO。numberOfSegments表示选项卡的个数。apportionSegmentWidthsByContent默认为NO，如果设置为YES，对于宽度为0的segment它将根据其内容自动调整segment的宽度。selectedSegmentIndex表示当前选中的segment的索引。 tintColor描述View中线条轮廓的颜色，它默认会一直从最底部的View向上层传递，直到某个子View修改了tintColor,传递链断开，新的tintColor继续向上层传递。更多关于tintColor和backgroundColor和foregroundColor的区别参考iOS字体颜色图片部分。
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对象方法
- (instancetype)initWithItems:(nullable NSArray *)items; // items can be NSStrings or UIImages. control is automatically sized to fit content
- (void)insertSegmentWithTitle:(nullable NSString *)title atIndex:(NSUInteger)segment animated:(BOOL)animated; // insert before segment number. 0..#segments. value pinned
- (void)insertSegmentWithImage:(nullable UIImage *)image atIndex:(NSUInteger)segment animated:(BOOL)animated;
- (void)removeSegmentAtIndex:(NSUInteger)segment animated:(BOOL)animated;
- (void)removeAllSegments;
- (void)setTitle:(nullable NSString *)title forSegmentAtIndex:(NSUInteger)segment; // can only have image or title, not both. must be 0..#segments - 1 (or ignored). default is nil
- (nullable NSString *)titleForSegmentAtIndex:(NSUInteger)segment;
- (void)setImage:(nullable UIImage *)image forSegmentAtIndex:(NSUInteger)segment; // can only have image or title, not both. must be 0..#segments - 1 (or ignored). default is nil
- (nullable UIImage *)imageForSegmentAtIndex:(NSUInteger)segment;
- (void)setWidth:(CGFloat)width forSegmentAtIndex:(NSUInteger)segment; // set to 0.0 width to autosize. default is 0.0
- (CGFloat)widthForSegmentAtIndex:(NSUInteger)segment;
- (void)setContentOffset:(CGSize)offset forSegmentAtIndex:(NSUInteger)segment; // adjust offset of image or text inside the segment. default is (0,0)
- (CGSize)contentOffsetForSegmentAtIndex:(NSUInteger)segment;
- (void)setEnabled:(BOOL)enabled forSegmentAtIndex:(NSUInteger)segment; // default is YES
- (BOOL)isEnabledForSegmentAtIndex:(NSUInteger)segment;
以上方法比较简单，根据方法名字就知道它的具体功能。需要注意的是initWithItems的数组参数既可以是字符串也可以是图片，segmentedControl会根据文字或者图片的宽高自动设置自己的宽高。setContentOffset设置图片或者文字内容相对于单个segment的坐标原点也就是左上角的偏移量，默认是(0,0).更多关于offset,inset的内容请参考iOS基本框架UIKit之几何形状setEnabled forSegmentAtIndex用来设置指定的索引的segment能否被选中。
- (void)setBackgroundImage:(nullable UIImage *)backgroundImage forState:(UIControlState)state barMetrics:(UIBarMetrics)barMetrics NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
- (nullable UIImage *)backgroundImageForState:(UIControlState)state barMetrics:(UIBarMetrics)barMetrics NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
- (void)setDividerImage:(nullable UIImage *)dividerImage forLeftSegmentState:(UIControlState)leftState rightSegmentState:(UIControlState)rightState barMetrics:(UIBarMetrics)barMetrics NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
- (nullable UIImage *)dividerImageForLeftSegmentState:(UIControlState)leftState rightSegmentState:(UIControlState)rightState barMetrics:(UIBarMetrics)barMetrics NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
- (void)setTitleTextAttributes:(nullable NSDictionary *)attributes forState:(UIControlState)state NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
- (nullable NSDictionary *)titleTextAttributesForState:(UIControlState)state NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
- (void)setContentPositionAdjustment:(UIOffset)adjustment forSegmentType:(UISegmentedControlSegment)leftCenterRightOrAlone barMetrics:(UIBarMetrics)barMetrics NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
- (UIOffset)contentPositionAdjustmentForSegmentType:(UISegmentedControlSegment)leftCenterRightOrAlone barMetrics:(UIBarMetrics)barMetrics NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
setBackgroundImage根据UIBarMetrics设置背景图片,barMetrics用于表示在手机屏幕横竖屏时对图片进行的拉伸和缩放以适应segment宽高的变化。
setDividerImage用于在你自定义SegmentControl的时候，必须设置左右两个segment都未选择时的分割图片，和左边选中右边为选中时的分割图片以及左边未选中右边选中时的分割图片这3种。
setTitleTextAttributes通过NSAttributedString.h头文件里面的UIKIT_EXTERN修饰的函数来设置文字的属性。更多关于UIKIT_EXTERN宏定义的内容参考iOS的宏定义
setContentPositionAdjustment主要用来对一些不同的segment类型内容通过offSet调整内容位置。segmentType有以下几种形式
typedef NS_ENUM(NSInteger, UISegmentedControlSegment) {
UISegmentedControlSegmentAny = 0,//带便任何一个segment
UISegmentedControlSegmentLeft = 1, // 最左边的segment,只有segment的个数大于1时才有效
UISegmentedControlSegmentCenter = 2, // 任何一个不是最左也不是最右的segment,只有当segment的个数大于2的时候才有效
UISegmentedControlSegmentRight = 3, // 最右边的segment,只有segment的个数大于1时才有效
UISegmentedControlSegmentAlone = 4, // 当且仅当segment的个数只有1个时才有效
};
下面是关于使用系统的UISegmentControl以及自定义SegmentControl(继承系统UISegmentControl)的一个Demo
